1. Field of the Invention
The present invention relates to a weighing system for conveyor borne articles. More particularly, the present invention relates to a weighing system for a high speed conveyor. Most particularly, the present invention provides a scale which weighs a conveyed article based upon the increase in conveyor belt friction due to the article's weight.
2. Description of the Prior Art
Industry has pressed automated package handling as a means to increase efficiency. This has been done largely through automated package identification by bar code labeling and automated sortation by scanners identifying the labels and routing the packages to the proper shipping area. However, one of the most common determining factors in material handling and sorting is package weight. Weight is an especially significant factor for the shipping industry where shipping fees are directly related to package weight. Little progress has been made in providing an automated means for accurately weighing conveyor borne packages as they travel at high speed through automated package identification and sorting systems.
The task of weighing packages to determine proper handling and/or labeling remains a low speed or manual operation. This does not present a problem for individuals or small businesses where the volume of materials handled is low. However, for larger businesses it would be desirable to have an automated means for accurate and high speed weighing of articles as they are carried by a conveyor for labeling and/or sorting.
Additionally, when individuals or small businesses ship packages through a local shipping office, this does not present as much of a problem to the shipping industry because the package is weighed and the shipping fees are paid directly to the carrier. However, the majority of package shipping originates from mail order businesses or companies which ship packages in large quantities. These bulk shippers generally have in-house facilities for weighing and labeling packages. In order for a shipping company to verify a package weight and the associated shipping costs, each package must be reweighed during shipping.
Typically, the shipping company transports the packages to a central location. The packages are then sorted by label as they move through a system of conveyor belts to the proper shipping areas. In order to verify shipping costs, the actual package weight can be measured and tracked against each shipping label. The volume of packages being handled at these locations renders manual weighing too time consuming.
The known conveyor weighing systems are generally not sensitive enough for high speed, accurate in-line weight verification of conveyor borne packages of mixed weights. This is due mainly to the fact that known systems generally measure the weight of an entire conveyor section, including the belt, pulleys, drives and supporting structure, along with the package, and then subtract the known weight of the conveyor section to calculate the package weight. This creates a speed limitation due to the time required to allow vibrations in the large resident mass to dampen or settle. It has been found that a scale of this type requires approximately 0.3 seconds to settle enough to get an accurate weight reading.
U.S. Pat. No. 4,276,112 illustrates one known conveyor scale. The conveyor includes a weighing section which calculates the weight of an object moving on the conveyor by taking the entire weight of the weighing conveyor section and the object and subtracting the known fixed weight of the conveyor to arrive at the package weight.
U.S. Pat. No. 4,729,442 teaches a similar system for weighing products on a conveyor by weighing an entire section of the conveyor along with the conveyed products.
U.S. Pat. No. 4,765,488 teaches a system of conveyors for sorting items by weight. This system utilizes conveyor belt weighing sections in which the entire conveyor belt section is weighed along with the conveyed object.
Due to the large resident mass of the scale components, these prior art systems generally do not provide the required sensitivity for weighing smaller packages travelling at high speed. Thus, the potential for error, along with the requirement for manual weight confirmation, is increased.